Field of the Invention
The invention relates to gear pumps for compressible liquids or fluids.
It relates more particularly to a new design for a pump structure, intended to achieve better pumping performance.
An advantageous application of the invention can also be found in its utilization in volumetric pumps, even though it can be applied to other types of pumps.
Description of the Related Art
There are several kinds of volumetric pumps, including those known as “synchronous gear” pumps and “self-driven” pumps.
Synchronous gear pumps comprise two pinions each equipped with peripheral teeth. In such pumps, the teeth of the two pinions do not touch one another. However, the teeth of the two pinions can be meshed with one another. Each of the two pinions is rotationally driven by a shaft. In other words, such pumps include two shafts for driving the pinions in rotation. Provision is then made for a gearbox in a sealed portion of the pump for synchronizing the rotation of the shafts. The teeth of the pinions for synchronous gear pumps are shaped such that rotation of the two pinions is allowed. The face of the teeth that is oriented towards the direction of rotation of the pinion is called “front face”. The other face of the teeth is called “rear face”.
Self-driven pinion pumps also include two pinions each equipped with evenly distributed peripheral teeth. In such pumps, one of the pinions (first pinion) is mounted on a rotationally-driven shaft. This first pinion drives the second pinion in rotation, by meshed contact of the teeth with one another. To this end, the teeth are thus shaped such that rotation of the two pinions is allowed. The front face of the teeth is then called “active face”. This is the face of the tooth of a first pinion that comes into contact with the face of a tooth of the other pinion, and that allows the other pinion to be rotationally driven. The other face of the tooth, i.e. the rear face, is also called “inactive face”.
The invention relates to self-driven pinion pumps.
Generally, pinions equipped with peripheral teeth in the form of lobes are found in synchronous gear pumps.
By “lobes” is meant teeth of a larger size, the end of which may have a curved shape. The radial projections of the gear wheels are called “teeth” when they are smaller, not so large as the lobes, with one end having a more pointed shape, or having sharp edges.
There are self-driven pumps that have pinions with lobes: one example of such a pump is described in particular in application FR 2 399 559.
For decades, in order to improve pump performance, persons skilled in the art have sought to modify the profile of the lobes or the teeth of the pinions. Persons skilled in the art have also sought to adjust the number of teeth or lobes of the gears. Furthermore, it has been demonstrated that the greater the number of projections (teeth or lobes) the pinion has, the better the mechanical drive. However, the greater the number of projections (teeth or lobes) the pinion has, the poorer the performance of the hydraulic drive.
Persons skilled in the art have often favoured the mechanical drive by utilizing gears with toothed pinions in self-driven pinion pumps.
Moreover, hybrid technical solutions, utilizing pinions with lobes and with teeth, have also been developed by persons skilled in the art in order to improve the hydraulic drive performance.
For example, document US 2014/0271313 presents a volumetric pump in which a three-lobed pinion and a three-toothed pinion intermesh with one another. As a result of the differences of shape and size of the intermeshed lobes and teeth, it is necessary for each shaft to have several stages of lobed and/or toothed pinions, angularly offset with respect to one another such that, when a first set of lobed and toothed pinions is no longer driven, a second set of lobed and toothed pinions takes over.
Such an embodiment does not give satisfactory pumping results, on account in particular of the necessary interchange between the different stages of lobed and toothed pinion sets, and on account of the leakage of liquid (or fluid) from one stage to another during pumping, unless radial fins are utilized between the pumping stages, preventing the fluid from leaking.